Audio system

ABSTRACT

Speakers for locating in a vehicle exhaust system having a speaker surround that is formed from a rubber compounded using a polyacrylate polymer. Speakers having a speaker surround that is integral with a coating that covers or substantially covers at least one surface of the diaphragm.

CROSS REFERENCE TO RELATED APPLICATION (S)

This application is a 371 National Phase Application of PCT PatentApplication No. PCT/EP2016/063194 file don Jun. 9, 2016 which claimspriority benefit of GB Patent Application No. 1513555.1 filed on Jul.31, 2015, which herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an audio system, in particular to anaudio system for use in a vehicle exhaust, and to speakers for use insaid audio systems.

BACKGROUND

It may be desirable to attach an audio system to a vehicle exhaust. Thisaudio system may be directed at two main goals. A first is so-calledengine harmonics addition (ASD). In other words, the speaker maygenerate noise so as to change or amplify the “revving” and/or runningsounds of an engine. This can be useful for amplifying quiet engines,enabling them to be heard, and for improving the sound of an engine toprovide, for example, a desirable v8 roar. A second is so-called engineharmonics cancellation, which may also be termed active noisecancellation (ANC). In this latter case, the audio system generatesanti-sound, thereby reducing the noise associated the revving andrunning of the engine.

However, the inside of an exhaust experiences high temperatures duringrunning of the vehicle. In diesel engines, the front of speaker mayexperience temperatures at high as 140° C., while in petrol engines thismay be as high as 160° C. These elevated temperatures can be maintainedfor long periods, for example, during long journeys. In addition,speakers themselves generate heat. Exhaust interiors also undergorepeated heating and cooling, as vehicles are used and then parked, usedand then parked repeatedly over their lifetime. In cold climates, cooltemperatures may be well below freezing for long periods in wintermonths.

Furthermore, the interior of a vehicle exhaust system is subjected to acocktail of assorted gaseous byproducts and particulates, includingincompletely combusted hydrocarbons, carbon monoxide, carbon dioxide,nitrogen oxides and sulfur compounds. These are often incompatible withand/or harmful to audio system components.

These extreme conditions limit the use of audio systems to alter carexhaust sounds. In particular, the current designs for loud speakers areunable to withstand the conditions within the exhaust system. As aconsequence, audio systems for vehicle exhausts are located outside theexhaust interior, for example attached to the outside of the exhaustpipe.

US2013/0202148 describes a muffler for an exhaust system. It is mountedin a housing on the exterior of the exhaust system, and the sound isallegedly transmitted and radiated into the exhaust stream via aconnecting pipe.

A similar arrangement is described in US2014/0328493.

SUMMARY

The present invention is based on the applicant's insight that throughuse of a suitable speaker surround, speakers may be placed in vehicleexhaust interiors. Specifically, the inventor has found that use of ahigh temperature rubber speaker surround permits speakers to be locatedproximal or within the exhaust gas flow, improving the performance ofaudio systems for use with vehicle exhausts (as the sound is generatedwithin the gas stream, rather than remotely). Speakers may be locatedwithin the vehicle exhaust flow, or adjacent to the flow without theneed for the protective flow restrictions (communicating pipes) used atpresent. Conventional rubbers are not suitable for use as speakersurrounds in vehicle exhausts because they are unable to withstand theextreme temperatures, while conventional high temperature speakers arebased on metal soldered components and are not gas tight (see, forexample, U.S. Pat. Nos. 5,581,624 A and 5,699,439).

In a first aspect, the present invention provides a speaker for locatingin a vehicle exhaust system, the speaker including a basket housing avoice coil and a spider and including a diaphragm, the diaphragm beingaffixed to the basket by a speaker surround, characterised in that thespeaker surround is formed from a rubber compounded using a polyacrylatepolymer. In other words, the rubber composition is based on apolyacrylate rubber, which is also referred to as an ACM rubber.

Suitably, the diaphragm is made from an aramid fiber material.Diaphragms made from these materials have been found to withstand theextreme temperature cycles experienced in a vehicle exhaust. Thediaphragm may also be made from a fibrous glass material (fiber glass).

It will be appreciated that, given the location of the speaker, gastightness is important. Suitably, the material is provided with acoating for gas tightness, for example, and not by way of limitation,the material may be coated with a polyester type of coating based onacrylic polyol and (iso)cyanate hardening agent.

It will be appreciated that good adhesion between the speaker surroundand diaphragm is very important in these applications. The inventor hassurprisingly found that the speaker surround of the invention providesexcellent adhesion between the speaker surround and cone material.Advantageously, the inventor has found that the speaker surround of theinvention is compatible with certain adhesives suitable for hightemperature use.

The inventor has observed that both the issue of gas tightness and theimportance of a durable and robust connection between the surround anddiaphragm may be efficiently achieved through use of overmolding, asdescribed herein. In other words, the speaker surround may beconcomitantly formed and attached to the diaphragm using an overmoldingtechnique.

In brief, using this overmolding process both forms the surround andcoats all or substantially all of at least one surface (inner or outersurface) of the diaphragm with the rubber. Suitably the diaphragm isformed of a fibrous material, for example, aramid fibre or glass fibre.Without wishing to be bound to any particular theory, the inventorbelieves that the rubber, during the overmolding process, penetrates thefibres of the diaphragm, This provides excellent adhesion between thesurround and the diaphragm, which the inventor has observed is able towithstand the challenging conditions experienced by the speaker in, forexample, a vehicle exhaust gas flow.

Furthermore, the rubber coating of the diaphragm has been found toreduce or even prevent gas permeability. In other words, the rubbercoating obviates the need for a separate gas tight coating to beapplied.

The surround assembly and consequently the moving mass of theloudspeaker produced using this overmolding technique may also belighter (˜5 g lighter on a 6.5″ assembly″) than speakers produced by theadhesive method described herein. This is because, at least, no adhesiveis needed. The rubber coating on the diaphragm portion may also belighter than other gas tight coatings likely to be applied.

Speakers produced using this overmolding technique are also more costand time efficient. This is because the production process may involvefewer steps and materials. For example, as the rubber coating obviatesthe need to apply a separate gas tight coating, the steps of applyingsaid coating and waiting for it to dry are avoided.

Furthermore, owing to the excellent adhesion, the application of aprimer (to assist adhesion between the diaphragm and surround) and thestep of waiting for the primer to dry can be avoided without sacrificingspeaker integrity and longevity.

These advantages when combined may halve the production cost per unit.

Accordingly, in some embodiments, the speaker surround is integral witha coating that covers or substantially covers at least one surface ofthe diaphragm. As described herein, both the surround and coating aretherefore formed from a rubber compounded using a polyacrylate polymer.Substantially covers refers to at least 75% by area of at least onesurface, more preferably at least 80%, more preferably at least 85%,more preferably at least 90%, more preferably at least 95%.

The other side of the diaphragm may also be at least partially coated,for example by a rubber flow along the surface during molding, orthrough penetration (strike through) of the rubber through the fibres.Preferably, only one face is covered or substantially covered, althoughspeakers in which both faces of the diaphragm are covered are within thescope of the invention.

Preferably, when the speaker is assembled, the entire exposed surface ofthe diaphragm is coated. The uncoated portion is suitably covered by adust cap. In other words, the speaker may further comprise a dust cap,wherein the dust cap conceals a portion of the diaphragm, wherein theconcealed portion is substantially free of rubber coating.

The inventor has observed that it is advantageous, in speakers having aseparate dust cap, for the portion of diaphragm covered by the dust capto be uncoated. This assists the assembly of the final speaker, as theinner diameter of the diaphragm (cone) can be accurately sized to fitover the coil without the need to estimate the extent to which rubberoverflow may alter the diameter.

It will be appreciated that the overmolding process described hereinalso permits the concomitant molding of a dust cap. Accordingly, in someembodiments the speaker further comprises a dust cap, wherein the dustcap is integral with the coating that covers or substantially covers atleast one surface of the diaphragm and is integral with the speakersurround.

It will be appreciated that dust caps are not typically used when thediaphragm of a speaker is flat, for example in flat panel loudspeakers.Accordingly, in some cases, the speaker does not have a dust cap and atleast one surface of the diaphragm is covered by a coating of rubbercompounded using a polyacrylate polymer, wherein the coating is integralwith the speaker surround. In some cases, the diaphragm of the speakeris flat and is covered by a coating of rubber compounded using apolyacrylate polymer, wherein the coating is integral with the speakersurround.

In some cases, the dust cap of the speaker is integral with thediaphragm.

While overmolding is advantageous, other adhesion processes may be used.The speaker surround of the invention surprisingly shows excellentcompatibility with certain adhesives based on epoxy resins. This affordsa speaker having the desired stability for this application. Thisrepresents a significant advantage when compared to EPDM-based rubbers(which are often described as being suitable for high temperatureapplications) as these have been shown to have compatibility issues withthese adhesives; this can lead to poor adhesion and therefore would leadto gas and particle ingress if used in a vehicle exhaust. Withoutwishing to be bound by any particular theory, the present inventorspeculates that the poor performance of EPDM is connected to too lowsurface tension. Unlike EPDM, the polyacrylate rubbers of the inventionhave acrylate groups along the polymer background that the inventorbelieves helps with adhesion.

Accordingly, in some embodiments, the speaker surround is glued to thebasket using an epoxy resin. In other words, an epoxy adhesive is used.In some embodiments, the speaker surround is glued to the diaphragmusing an epoxy adhesive. Epoxy adhesives are known in the art.

The or each epoxy adhesive may suitably be a heat curing epoxy adhesive,for example a one-component heat curing epoxy adhesive. For example, theepoxy adhesive may be based on a bisphenol diglycidylether (such asbisphenol A diglycidylether), suitably having a molecular weight of≤700. For example, the adhesive may be a one-part heat curing epoxyadhesive based on an oligomeric mixture of bisphenol A diglycidylether(molecular weight ≤700).

It will appreciated that an adhesive to join the diaphragm and speakersurround is not essential. For example, the diaphragm and surround maybe joined using overmolding or insert (occasionally referred to asinset) molding techniques, which may be beneficial for efficiency duringmanufacture. For example, the rubber may be injection molded over theedge of the diaphragm so that the rubber cures into the diaphragm fibers(insert molding). The rubber may also be molded over the edge of thediaphragm using compression molding techniques. Combinations of insertand compression molding may also be used. Suitably, the edge of thediaphragm to be inset in the rubber is first coated with an adhesionpromoter.

Suitably, the basket is made of a metal material, for example, a metalalloy such as steel. In some cases, the basket is stainless steel ore-coated steel.

As is conventional, the rubber of the speaker surround may be compoundedwith a filler, which may be one or more of carbon black, silica, andclay to suit. The filler may be present in an amount from 20 to 120 PHR(with respect to the ACM polymer). For example, the amount of filler maybe 30 to 100 PHR, for example, 40 to 90 PHR, for example, 50 to 80 PHR.In some cases, it is around 65 PHR. Carbon black may be used alone.Carbon black may also be mixed with clay. This can reduce costs.

Suitably, the rubber undergoes less than a 20% change in E-modulus whenthe temperature is varied from 25° C. to 150° C.

Suitably, no weight loss in the rubber is detected inthermogravimetrical analysis at temperatures below 250° C.

As described herein, the speakers of the invention are for locating in avehicle exhaust system. In a further aspect, the invention provides avehicle exhaust system comprising a speaker as described herein.

The present invention further provides audio systems for generatingsound in a vehicle exhaust, the audio system comprising a speakeraccording to the first aspect, a detector and a processor, wherein thedetector is configured to detect engine noise and generate a firstsignal, the processor is configured to receive the signal and send asecond signal to the speaker causing sound waves to be produced by thespeaker.

The detector may be a microphone, or may electronically detectaccelerator depression and/or engine activity.

In some embodiments, the microphone is located inside the vehicleexhaust.

The processor may be configured to determine the volume and frequency ofsound to be produced, for example, by means of a computer program.

In some cases, the sound waves produced increase the volume of the noisecoming from the exhaust. This may be termed ASD. In some cases, thesound waves produced decrease the volume of the noise coming from theexhaust. This may be termed ANC.

It will be appreciated that the sound waves may also moderate theapparent tone or pitch of the engine, for example, to produce acharacteristic engine purr.

The overmolding process described herein is useful for speakers forlocating in a vehicle exhaust system and other similarly hightemperature applications. However, the advantageous gas tightness of thecoating which is achieved efficiently and cost effectively has utilityfor other, non-high temperature, speaker applications. In other words,the invention further relates to a speaker including a basket housing avoice coil and a spider and including a diaphragm, the diaphragm beingaffixed to the basket by a speaker surround wherein the speaker surroundis integral with a coating that covers or substantially covers at leastone surface of the diaphragm.

Suitably, no adhesive is used to affix the diaphragm to the speakersurround; the integral nature of the surround and coating insteadprovides an effective connection.

It will be appreciated that for these non-high temperature applications,the use of compounded polyacrylate rubber is optional. Other thermosetrubbers, for example, NBR (nitrile butadiene), EPDM (ethylene propylenediene terpolymer), IIR (isobutylene isoprene rubber), PUR (polyurethanerubber), CSM (chlorosulfonated polyethylene), CPE (CM;chloropolyethylene), AEM (Ethylene acrylic rubber), ECO(epichlorohydrin) may be used. Thermoplastic Elastomers or vulcanisatesincluding TPE (thermoplastic elastomer), TPV (thermoplasticvulcanizate), TPU (thermoplastic polyurethane), may also be used.

The inventor has found that such overmolded coatings, whether usingcompounded polyacrylate rubber or another material as described herein,make efficient use of material, providing only a relatively thincoating. Advantageously, only one face of the diaphragm is typicallycoated. In some cases, the coating is provided only to the front face ofthe diaphragm (although it will be appreciated that some strikethroughof the coating through the interstitial holes of the fibrous diaphragmmaterial may result in some material forming on the reverse). In thiscontext, front face refers to the outwards facing surface when thespeaker is assembled.

Preferably, the thickness of the coating(s) is between 5 and 60% of thethickness of the diaphragm material. For example, suitably the thicknessof the coating on the or each diaphragm face is less than 60% of thethickness of the cone material, for example less than 50%, less than40%, less than 30%, less than 25%, less than 20%, less than 15%, or evenas low as less than 10%. Where there is some variation in thickness, thevalues refers to a mean average.

In certain non-limiting embodiments, the speaker has a diaphragm of0.3-0.4 mm thickness and the coating, applied to the front face of thecone only, is between 20 and 200 μm.

In a further aspect, the present invention provides use of a compoundedpolyacrylate rubber in a speaker.

It will be appreciated that the speakers and audio systems describedherein are suitable for use in a vehicle exhaust. Naturally, they arenot limited to use in vehicle exhausts and are suitable for other,similarly extreme temperature, locations.

The invention will now be described with reference to followingdrawings, in which:

FIG. 1 shows a partial cut away speaker according to the invention.

FIG. 2 shows a representative partially cut away drawing of the speakerin situ in an exhaust system.

FIG. 3 shows the variation in tensile strength of the ACM rubber used inthe speaker surround of the present invention and a comparisonEPDM-based rubber.

FIG. 4 shows changes in E-modulus, tensile strength and elongation afterheat exposure at various temperatures for various durations.

FIG. 5 shows the DMTA of the ACM rubber used in the speaker surround ofthe present invention in a temperature sweep from −100° C. to +200° C.with 1 Hz frequency.

FIG. 6 shows the TGA of the ACM rubber used in the speaker surround ofthe present invention.

FIG. 7 shows a speaker according the invention and a comparator speakerafter a high power capacity handling test at 160° C.

FIG. 8 shows an illustration of a mold that may be used to cast anintegral surround and diaphragm coating as described herein.

DETAILED DESCRIPTION

The following description is provided to illustrate the invention. It isnot intended to limit the invention.

The invention relates to a speaker, which may be as illustrated inFIG. 1. The speaker is suitable for using in vehicle exhaust systems,where it is exposed to high temperatures and extreme atmosphericconditions. The speaker depicted in FIG. 1 is a 100 W subwoofer andincludes a yoke 1 (referred to as a U or T yoke) which is formed ofe-coated steel. This supports a magnet 2 and a voice coil 3 which isformed of insulated aluminium (the insulation is provided by paper oraramid fiber material). The speaker has a metal basket 4 formed ofe-coated steel which surrounds the voice coil 3. Between the speaker andmagnet is a washer 5 of e-coated steel. The washer is glued to the yokeand magnet. Inside the basket 4 is a spider 6 formed of aramid fibermaterial and glued to the inner wall of the basket. A lead wire 7 isprovided and attached to a connector plate with tags on the baskethousing. The speaker has a diaphragm 8 (often referred to as a cone)over the opening of the basket, towards the “front” of the speaker. Thisis formed of aramid fiber material. The back of the cone is in contactwith the voice coil 3 such that motive force generated by the voice coilis transmitted to the cone. The voice coil 3 is protected by a dust cap9 of aramid fiber material to prevent ingress of exhaust fumes,condensates and particulates during use. The speaker has a speakersurround 10 around the circumference at the basket opening. This speakersurround is formed of a rubber compounded using a polyacrylate polymer.In other words, the rubber composition of the speaker is based on apolyacrylate polymer—the rubber is an ACM rubber. The cone is adhered tothe speaker surround 10 at a location 11 around the entirecircumference. The adhesion is achieved by a high temperature adhesive.The speaker surround is glued to the basket edge at a location 12 aroundthe entire circumference.

In situ, the speaker is located in a vehicle exhaust system, with thefront of the speaker directed into the engine emission stream. Thistypically includes exhaust fumes (such as CO_(x), NO_(x), SO_(x)),extremely acidic gasoline or diesel condensate and incompletelycombusted hydrocarbons. The front of the speaker may therefore beexpected to experience temperatures of 160° C. during use, while theback (magnet) portion may experience temperatures of 125° C. owing tothe engine system, rising to 140° C. as the magnet operation itself maygenerate heat. During operation, the voice coil may generate up to 65°C. of heat, in addition to that experienced as a result of the vehicleoperation.

The speaker may be controlled by a processor (not shown) which in turnreceives information from a detector (not shown). The interfaces andconnections between the detector, processor and speaker may be wired orwireless.

Of course, it will be appreciated that other appropriate speakerarrangements may be used, either as described herein or as is apparentto a person skilled in the art. For example, and not by way oflimitation, the diaphragm 8 and speaker surround 10 may be inset moldedtogether such that no adhesive is used. The speaker shown and describedis circular, however, other appropriate shapes and arrangements may beenvisaged. Except where specified otherwise, for example, in the claims,other suitable materials may be used. For example, stainless steel mayreplace e-coated steel.

The speaker of FIG. 1 is locatable in a vehicle exhaust system. Variouslocations and methods for installing a speaker arrangement in an exhaustsystem will be apparent to the skilled person. FIG. 2 shows anon-limiting possible arrangement. FIG. 2 a portion of a vehicle exhaustsystem comprising a pipe 100 through with exhaust gases flow. The pipe,and therefore exhaust gases, are in fluid communication via tube 101with a speaker unit 102 housing a speaker 103 according to theinvention. To assist pressure equalization, a pressing equalising tube104 may be provided.

Of course, it will be appreciated that the speaker may be provided in achamber in the exhaust system, with the exhaust gasses flowing throughsaid chamber. Advantageously, there is no need to provide a filter toprotect the speaker from the exhaust gasses.

Abbreviations

-   ACM-polyacrylate polymer-   ANC-engine noise cancellation-   ASD-engine harmonics addition-   DMTA-dynamic mechanical thermal analysis-   EPDM-ethylene propylene diene polymer-   EPHR-chemical equivalents per hundred of rubber-   PHR-parts per hundred of rubber-   T_(g)-glass transition-   TGA-thermogravimetrical analysis    Definitions    Aramid fiber material

This describes a class of materials formed of strong, heat-resistantfibers. These fibers are produced by spinning solid fibers from a liquidchemical blend of aromatic polyamides.

For example, the aramid fiber material may comprise a para-aramid suchas Kevlar® or a meta-aramid such as Nomex®.

Parts Per Hundred of Rubber

This is a commonly used way of describing the relative amounts of thevarious components in a compounded rubber. It refers to relative amountsof starting materials that are compounded with respect to the polymerused (the ratio of which is set to 100). In other words, 5 PHR of aningredient means that 5 kg of this ingredient is added 100 kg ofpolymer.

Vulcanisation/Curing

This is the chemical process of cross-linking a rubber composition toprovide a more durable material. Vulcanization is typically achievedwith sulfur. For example, for high temperature rubbers such as EPDMrubbers, o-toluidines such as DOTG are commonly used. However,o-toluidines have recently been added to EU REACH candidate list ofsubstances for very high concern for authorisation owing to theircarcinogenic properties. Advantageously, the rubbers of the presentinvention are cured without the use of o-toluidines.

Rubber Compositions

The rubber of the speaker surround is compounded using an ACM polymer.

Polyacrylate polymer, also referred to as ACM polymer, is formed from amonomer composition comprising acrylic acid ester units. It may beformed from a monomer composition comprising only acrylic acid esterunits. However, small amounts of monomers other than acrylic acid esterunits may be present. Suitably, the composition comprises 90 to 99.9% byweight acrylic acid ester monomer units. Suitably, the compositioncomprises 60-90% by weight, optionally 70-90% by weight, for example,about 80% by weight alkyl acrylate monomers. Suitably, at least half ofthe alkyl monomer is ethyl acrylate monomer. Suitably, the ethyl acetateis copolymerised with other acrylate esters. Suitably, the compositionmay comprise 40 to 70% by weight ethyl acrylate, for example 50 to 60%by weight. A representative value is around 50% by weight ethylacrylate. Suitable other acrylate esters include n-butyl acrylate and2-methoxyethyl acrylate.

The composition may comprise 0.1 to 10% by weight at least one carboxylgroup-containing ethylenically unsaturated monomer, for examplemono-n-methyl maleate or mono-n-methyl fumarate, and/or a monomercomprising a reactive halogen such as vinyl chloroacetate. This may bereferred to as a functionalised monomer. For example, the compositionmay comprise 1 to 5% by weight functionalised monomer. More than onefunctionalised monomer may be present. For example, a mixture of chloroand carboxyl groups may be present in the polymer.

In some embodiments, the ACM polymer is not a “dual cure-type” polymer(in other words, it is substantially free of carboxyl groups). In someembodiments, the composition does not comprise a monomer comprising areactive halogen.

The polymer may be of the HT-ACM family, which is configured for amidecrosslinking technology using curatives as described herein.

Suitable ACM polymers are known in the art, and may be manufacturedaccording to known methods (for example, as described in EP1378539,which is incorporated by reference in its entirety) or purchased fromcommercial suppliers, for example Hy-Temp AR12® and Hy-Temp AR12B® fromZeon Chemicals®.

In the quantities described herein, all values are given in PHR withrespect to 100 parts to this ACM polymer.

It will be appreciated that the rubber is compounded with additionalingredients, including a filler as described above. The followingingredients may be included in the compounding. It will be appreciatedthat ingredient combinations may be selected to complement each otherand/or to behave synergistically.

The rubber of the speaker surround is compounded with an antioxidant.Any suitable antioxidant may be used, and such antioxidants are known inthe art. Suitably, the antioxidant is present in an amount from 0.5 to 5PHR, for example, from 1 to 5 PHR. A representative value is around 3.5PHR.

The antioxidant may be a diphenyl amine, for example 4,4′-bis (alpha,alpha-dimethylbenzyl) diphenylamine. This is available commercially asNaugard® 445 from Chemtura®.

More than one antioxidant may be present. For example, an imidazole maybe used. Imidazoles have well-known corrosion inhibitor properties. Theimidazole may be a benzimidazole, for example an alkylmercaptobenzimidazole. A suitable further antioxidant ismethylmercaptobenzimidazole, available commercially as Rhenogran®MMBI-70 from RheinChemie Additives®. For example, a diphenylamineantioxidant and a mercaptobenzimidazole antioxidant may be used in aratio of approximately 4:3.

The inventor has found that methylmercaptobenzimidazole is aparticularly suitable anti-oxidant and it retains its properties anddoes not interfere in the ACM curing and vulcanising processes. Withoutwishing to be bound by any particular theory, the inventor attributesthis to the absence of metal cations, and in particular, zinc (ZMBI—zincmercaptobenzimidazole is commonly used in the art).

The rubber of the speaker surround is compounded with stearic acid, asis known in the art. Stearic acid may help to dissolve the curatives.The stearic acid may be present in an amount from 0.5 to 3 PHR, forexample, around 1 PHR.

Processing aids are normally included to improve the handling of therubber during compounding and molding. Suitable processing aids areknown in the art. The total amount of processing aids may be up to about10 PHR, for example up to about 6 PHR. For example, the total amount ofprocessing aids may be 0.5 to 6 PHR.

More than one processing aid may be used. For example, a processing aidmay be added to improve mold release and a processing aid added toimprove the mixing and compounding of the rubber product. By way ofexample, and not by way of limitation, long chain (for example C₁₅₋₂₅)primary alkyl amines may be used such as octadecyl amine. This isavailable commercially as Ofalub® STA available from ChemSpec Ltd® andArmeen® 18D from AkzoNobel®. By way of example, and not by way oflimitation phosphoric acid esters of modified fatty alcohols may be usedsuch as commercially available Ofalub® SEO available from ChemSpec Ltd®.

Plasticizers can be used to improve processing of the compounded rubber.These plasticizers also transfer beneficial properties to the coldflexibility of the compounded rubber. By way of example, and not by wayof limitation, a, plasticizer like TOTM (Trioctyl Trimellitate) may beused to improve the molding process.

Importantly, as described herein, a sulfur vulcanisation is not used.This is advantageous as it avoids the use of hazardous o-toluidenereagents. Rather, suitable curing can be achieved using appropriatecuratives. Suitably, the rubber of the speaker surround is compoundedwith a carbamate. This may be present in an amount from 0.1 to 6 PHR.More than one carbamate may be present. Suitably, the carbamate is acarbamate of an α,ω-diaminealkane, for example hexamethylene diaminecarbamate. Hexamethylene diamine carbamate is commercially available asA representative amount range for this α,ω-diaminealkane carbamate is0.1 to 2 PHR. Without wishing to be bound to any particular theory, itis thought that the carbamate generates an α,ω-diamide cross-linkbetween two polymer backbones of the ACM polymer (for example, throughester to amide nucleophilic amide substitution). Further curing itsthought to cause these diamide cross-linkers to react with adjacentester moieties on the polymeric backbones, leading to dehydration andimide formation.

Commercially available combinations of activated amines may be used inthe curing process. Again without wishing to be bound to any particulartheory, it is thought that these activated amines assist withamide/imide bond formation by generating leaving groups. Thiscomposition comprising activated amines may be present in an amount from1 to 4 PHR, for example, a representative amount is around 2 PHR. Acommercially available example is Rhenogran® XLA-60 (GE2014), availablefrom Lanxess®.

As described above, the curing process suitably uses amide crosslinkingtechnology. Suitably, the curing process involves the formation ofcarbon-nitrogen bonds. Suitably, after curing the rubber comprisescross-linked portions comprising amide and/or imide bonds. Preferably,imide bonds are present.

It will be appreciated that the present invention further relates to arubber as described herein.

It will be appreciated that relative amounts of many of theseingredients may be varied. A representative compounding formulation isshown below:

Chemical Min Max ACM (polyacrylate rubber) polymer 100.00 100.00 Carbonblack 0.00* 120.00 Silica 0.00* 60.00 Clay 0.00* 50.00 A diphenylaminesuch as 4,4′-Bis 0.50 4.00 (α,α-dimethylbenzyl) diphenylamine(Antioxidant) Stearic acid 0.50 3.00 Octadecyl amine (process aid) 0.253.00 Phosphoric acid ester of modified fatty 0.25 3.00 alcohol (processaid) Combination of activated amines 1.00 4.00 Hexamethylene DiamineCarbamate 0.10 2.00 Methylmercaptobenzimidazole (antioxidant) 3.00*Typically one or more of these filler will be present, that is therewill be at least 20 PHR of carbon black, silica and/or clay.

It will be appreciated that the rubber may be compounded with additionalingredients such as plasticizers and dyes (if silica is used as fillerfor example).

For example, TOTM (Min 0.50; Max 5.00) may preferably be added to theabove composition.

EXAMPLE 1

Example Rubber Composition

The following is a representative rubber composition according to thepresent invention. It is referred to as Example 1.

Trade name of Chemical example Amount ACM (polyacrylate rubber) polymerHyTemp AR12B 100.00 Carbon black 65.00 Antioxidant (diphenylamine)Naugard 445* 2.00 Stearic acid 1.00 Octadecyl amine Ofalub STA 1.00Armeen 18D Phosphoric acid ester of modified Ofalub SEO 1.00 fattyalcohol Combination of activated amines Rhenogran 2.00 XLA-60Hexamethylene Diamine Carbamate Diak-1 0.60 Antioxidantmethylmercaptobenzimidazole Rhenogran 1.43 MMBI-70 *(4,4′-bis (alpha,alpha-dimethylbenzyl) diphenylamine)

As elsewhere, all values mentioned are parts per hundred of rubber (PHR)with respect to a ratio of 100 parts of polymer (ACM).

The rubber was compounded using conventional rubber mixing equipmentusing techniques well established in the art. Where appropriate,processing to provide the rubber edge (surround) was achieved byinjection molding or via thermoforming (compression moulding). Thesetechniques are known in the art.

Comparison EPDM Rubber Composition

A comparison rubber speaker surround was prepared using the followingEPDM-based formulation:

Chemical Trade name/Abbreviation Amount EPDM polymer JSR/EP33 100 carbonblack N550 15 carbon black N774 10 calcium carbonate CACO3 20 clayKA0LINE 30 silica 1106 15 plasticizer ATBC 10 stearic acid ST 1.5curative TBZTD 0.5 curative EZ 0.6 zinc oxide ZNO 5 sulfur S 1.5antioxidant RD 1.5Tensile Strength

The rubbers of the invention show excellent retention of tensilestrength over a wide temperature range. Indeed, as can be seen from FIG.2, the tensile strength hardly changes over a 125° C. window. Thisprovides excellent mechanical stability and integrity for theapplications of interest. By contrast, a compassion EPDM-based rubbermarketed for high temperature use shows marked variation in tensilestrength over the temperature range.

The tensile strength of the rubbers of the invention are also stableafter prolonged exposure to high temperature. FIG. 3 shows the changesin E-modulus, tensile strength and elongation after heat exposure atvarious temperatures for various durations. Importantly, the tensilestrength is virtually unchanged, even after 96 h at 170° C.

Thermal Analysis

FIG. 4 shows the DMTA of the rubber of example 1 in a temperature sweepfrom −100° C. to +200° C. with 1 Hz frequency: static strain was set at0.13% and dynamic amplitude was 0.04%. The glass transition area isbetween −35° C. and +15° C.; with a T_(g) (glass transition) of around−10° C. This is measured in shear and is not representative for actualT_(g). Actual T_(g) can be determined by DSC and is typically some 15°C. lower than on DMTA.

FIG. 5 shows the TGA of the rubber of example 1. The temperature wasincreased from 40° C. to 600° C. at 20° C./min under an N₂ inertatmosphere. The temperature was cooled to 450° C. at 20° C./min; thenthe gas supply switched to an O₂ atmosphere, and the temperatureincreased at 20° C./min up to 850° C.

As is clear from the curve, there is no ash content (no inorganicfillers were used). The first weight loss appeared only around 300° C.This is very high and shows stable performance for this temperaturerange.

Structural Integrity of Speaker Surrounds

The rubber of example 1 was tested as a molded speaker surround andcompared to a conventional EPDM based surround in a high power capacityhandling test. A sinusoidal wave of 45 Hz was put on the speaker with apower of 7.5V (free air). These tests were performed at differenttemperatures. The comparison speakers fail at 160° C.: the rubber edgeis completely scattered. Speakers of the invention have passed this testeven at 180° C. (higher temperatures are now being tested and initialresults are promising).

FIG. 6 shows the speakers before and after the test performed at 160° C.

Advantageous Properties

The rubber of example 1 has been shown to:

-   -   i. Maintain dynamic behaviour over the entire temperature range        of interest (−40° C. to +200° C.). Early results suggest that        this upper limit is much higher.    -   ii. Provide adhesion to the cone material.    -   iii. Satisfy requirements for use in a vehicle exhaust (ability        to withstand exhaust fumes, gas impermeability etc)    -   iv. Be compatible with suitable high temperature resistant        adhesives

Advantageously, the rubbers of the invention are compounded entirelysulfur free, meaning that o-toulidines are not used. As explained above,o-toulidines have recently been placed on the EU REACH candidate list ofsubstances for very high concern for authorisation. The inventionprovides suitable rubbers for high temperature uses while avoiding theuse of o-toulidines such as DOTG.

Integral Surround and Diaphragm Coating

As described herein, the inventor has found that it may be advantageousto use rubber as described herein to form both the speaker surround andto provide a coating to substantially all of at least one face of thediaphragm. This serves to improve the durability and longevity of thespeaker as the connection of the surround and diaphragm is integral, andreduces both unit cost and weight (as fewer materials and process stepsare used). The rubber may coat one or both faces of the diaphragm, andsuitably partially or completely strikes through gaps between the fibresof the cone material. The inventor has found that the resultantspeakers, once assembled, show desirable gas tightness without the needfor a separate gas tightness layer or other gas tightness treatmentstep. In other words, suitably the speaker diaphragm is not treated withphenolic resin, acrylic polyol and (iso)cyanate hardening agent orsimilar.

A representative mold is shown in FIG. 8. The mold has an upper portion200 and a lower portion 201. The upper and lower portions define acavity 202. The diagram shows a cross section, and the cavity, for thepurpose of this explanation, should be considered circular. Of course,as described herein, other speaker shapes are also envisaged. Thediaphragm is placed in cavity 202 and is indicated by a dotted line. Thecavity further comprises an annular 203 region into which the surroundis cast. As shown, the diaphragm does not extend into the surroundregion, which may have a curve, as shown.

The diaphragm and mold cavity are centred on a centering portion 204which ensures that the relevant pieces are in alignment when the rubberis molded. The upper and lower portions as shown are held togetherduring the molding process by compression, although other meansincluding bolts and clamps will be apparent to the skilled person.

As shown, the rubber is injected under pressure via conduit 205. Onlyone is shown, although typically there will be more than one spacedaround the mold. The rubber may be introduced by injection moldingprocesses, but other rubber molding processes may be used, for examplethermoforming/compression molding in which thin strips of rubber areplaced in the mold and cast through application of heat and/or pressure.

The neck portion of the cone is preferably protected by a seal, suchthat a small section of the cone at the neck (which is covered by thedust cap in the assembled speaker) is not overmolded. Keeping thissection of the cone free of rubber coating improves adhesion of the coneneck to coil. The inventor has further observed that shielding the neckportion helps to prevent rubber pooling and collecting at the neck area.

The seals may be in the form of O-rings 206, and may be provided aboveand/or below the cone material. The inventor has observed that the useof square-cut O-rings may provide a more efficient seal against thediaphragm material. Suitable sealing materials may include, but are notlimited to, Viton®, silicone, Teflon® NBR and steel.

After forming the integral surround and coating, preferably, the rubberis at least partially cured in the mold. This may prevent damage to theassembly when it is removed.

All optional features and preferences described herein are combinable tothe extent that such a combination is not clearly excluded.

The invention claimed is:
 1. A speaker for locating in a vehicle exhaustsystem, the speaker including a basket housing a voice coil and a spiderand including a diaphragm, the diaphragm being affixed to the basket bya speaker surround, characterised in that the speaker surround is formedfrom a rubber compounded using a polyacrylate polymer and wherein thediaphragm is formed of a fibrous material, the speaker surround beingintegral with a coating that covers or substantially covers at least onesurface of the diaphragm, and the speaker surround and coating beingformed by use of an overmolding process.
 2. The speaker of claim 1,wherein the diaphragm is formed of an aramid fibre material orfiberglass.
 3. The speaker of claim 1, wherein the speaker furthercomprises a dust cap, wherein the dust cap conceals a portion of thediaphragm, wherein the concealed portion is substantially free of rubbercoating.
 4. The speaker of claim 1, wherein the speaker furthercomprises a dust cap, wherein the dust cap is integral with the coatingthat covers or substantially covers at least one surface of thediaphragm and is integral with the speaker surround.
 5. The speaker ofclaim 1, wherein the speaker further comprises a dust cap which isintegral with the diaphragm.
 6. The speaker of claim 1, wherein thespeaker surround is secured to the basket using a heat-cure epoxyadhesive.
 7. The speaker of claim 1, wherein the rubber is compoundedwith an alkyl mercaptobenzimidazole, optionally wherein the rubber iscompounded with methyl mercaptobenzimidazole.
 8. The speaker of claim 1,wherein the rubber is compounded with both carbon black and clay.
 9. Anaudio system for generating sound in a vehicle exhaust, the audio systemcomprising a speaker according to claim 1, a detector and a processor,wherein the detector is configured to detect engine noise and generate afirst signal, the processor is configured to receive the signal and senda second signal to the speaker causing sound waves to be produced by thespeaker.
 10. A speaker including a basket housing a voice coil and aspider and including a diaphragm, the diaphragm being affixed to thebasket by a speaker surround wherein the speaker surround is integralwith a coating that covers or substantially covers at least one surfaceof the diaphragm the speaker surround and coating being formed by use ofan overmolding process, and the diaphragm being formed of a fibrousmaterial.
 11. The speaker of claim 10, wherein the coating covers orsubstantially covers only one surface of the diaphragm.
 12. The speakerof claim 10, wherein the coating thickness is 60% or less than thethickness of the diaphragm.
 13. The speaker of claim 10, wherein thespeaker further comprises a dust cap, wherein the dust cap is integralwith the coating that covers or substantially covers at least onesurface of the diaphragm and is integral with the speaker surround. 14.The speaker of claim 10, wherein the speaker further comprises a dustcap, wherein the dust cap is integral with the diaphragm.